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Statistical Methods for Coexistence in Future Wireless Networks

Periodic Report Summary 1 - COEXIST (Statistical Methods for Coexistence in Future Wireless Networks)

The limited number of available frequency bands is a strong barrier to the growth of new ICT services. To solve this fundamental problem of spectrum scarcity, government regulatory bodies recently started to review their spectrum allocation policies proposing opportunistic spectrum access (OSA). This project has addressed the problem of wireless networks coexistence in the context of OSA which enables multiple networks to share the same radio spectrum. The priority in accessing the radio channel identifies primary and secondary networks, which have the higher and the lower priority respectively. The activity of the secondary network using OSA and the effect of the aggregate interference injected into the primary network are mutually dependent, and they are influenced by the spatial positions of both primary and secondary users. Therefore the geometry of the networks plays an important role for spectrum usage optimization. This project developed a theoretical framework using stochastic geometry tools that enable to address network coexistence problem with a detailed model of the aggregate interference in multi-tiers networks accounting for the activity and the random displacement of the nodes of all the coexisting networks. The project analyzed the network coexistence in different scenarios and in particular it considered the case of the deployment of a network of small-cells, which are deployed to increase the coverage and capacity of the cellular network. In this scenario, the project analyzed of strategies for an optimal use of the resources and the network throughput.

Among the results of this project the following can be highlighted:
• The quantification of the impact of the secondary access point discovery performance on the the uplink capacity of the small cells located in the Voronoi cell of a macrocell base station. The proposed mathematical formulation allows accounting for the uncertainties associated with random position, density, user activity, propagation channel, network interference generated by uncoordinated activity, and the sensing scheme implemented by the mobile devices.
• The definition of a fundamental limit on the interference density that allows robust detection and the relation between energy efficiency and sensing time using large deviations theory.
• The formulation of several optimization problems that yields design guidelines for energy efficient small cell networks.
• The development of an analytical framework to evaluate the statistical performance of multi-tier heterogeneous networks with successive interference cancellation (SIC) capabilities, accounting for the computational complexity of the cancellation scheme and the relevant network related parameters such as the random location of the access points (APs) and mobile users, and the characteristics of the propagation channel.
• The derivation of expression for the success probability to cancel the nth strongest signal and to decode the signal of interest (SoI) showed that when users are connected to the AP which provides the maximum long-term received signal power, the analysis indicates that the performance We extend the statistical model to include several association policies where distinct gains of SIC are expected: (i) maximum instantaneous SIR association, (ii) range expansion, and (iii) minimum load association.
• The quantification of the beneficial effect of the coexistence of heterogeneous network on communication secrecy.
• The definition of a new coexistence paradigm where the mutual interference generated by concurrent communication links increase the network communication secrecy.